1. Field of the Invention
This invention relates generally to electric, submersible pump assemblies and relates particularly to a pump assembly having an internal re-priming system.
2. Description of the Related Art
A conventional, electric, submersible pump (ESP) assembly includes an electric motor and a pump that is used to pump oil or other fluids within a wellbore. The electric motors have a rotatable rotor that is contained within a stationary stator. The rotors for the submersible pumps are usually disposed in substantially vertical position by virtue of their placement in wellbores, which typically are vertical shafts. Therefore, during operation, the rotor shaft of the motor is oriented in the vertical position. The motor is connected by a cable or other means to a source of electricity for powering motor.
The motor is used to operate the pump, which is typically a centrifugal pump having a plurality of stages. Each pump stage has an impeller mounted to a central shaft for rotating the impeller within a corresponding diffuser. The shaft of the motor is coupled to the shaft of the pump, and the pump stages impart an upward force to the fluid when the central shaft is rotated.
For a centrifugal pump to operate, the pump must maintain its xe2x80x9cprime,xe2x80x9d in which fluid is located in and around the xe2x80x9ceye,xe2x80x9d or central intake portion, of the first impeller. If gas is located in the intake, for example, if a gas slug moves through the well to the pump, the pump may lose its prime, preventing the pump from pumping while gas remains around the eye of the pump. The pump can be re-primed by moving fluids to around the intake for the first impeller, and the pump will begin operating again.
While it is known in the art to provide self-priming centrifugal pumps, many of these rely on a fluid storage chamber or reservoir to provide fluid for re-priming, for example, in U.S. Pat. Nos. 2,553,066, 3,276,384 and 3,381,618. However, it is desirable to eliminate the need for a reservoir by using the fluids in the riser to automatically actuate a valve to re-prime the pump when the pump pressure falls.
A submersible pump assembly has a pump and a valve. The pump has an inlet and an outlet and at least one pump stage for pumping well fluids from the pump inlet to the pump outlet. The valve has an inlet, an outlet, and a valve member, the inlet of the valve being connected to the pump outlet, the outlet of the valve being connected to a conduit for conducting well fluids to a desired location. The valve member is vertically movable between a pumping position and a priming position, the valve member being biased toward the priming position. A priming conduit connects the outlet of the valve to the inlet of the pump, the priming conduit having an outlet located near the pump stage for directing well fluids flowing through the priming conduit into an intake of the pump stage.
When the pump stage is pumping well fluid, the valve member is moved by well fluid pressure to the pumping position, in which well fluids flow from the inlet of the valve to the outlet of the valve. In the pumping position, the valve member prevents well fluids from flowing into the priming conduit.
When the pump stage is not pumping well fluid, the valve member returns to the priming position, in which well fluids flow from the outlet of the valve, through the priming conduit, and into the pump inlet for priming the pump.